The ResQMe is a cheap glass breaker and seat belt cutter that you can stash anywhere in case of emergency.

One of the many things you should always keep in your car is a way to escape should you get trapped after a collision. At only $10, the ResQMe is a cheap but effective safety measure for any accident—whether your car's flipped over or sinking in a lake. What makes this particular tool different from others is that it's two tools in one: it'll not only break your safety windows when your doors won't open, but it has a sheathed knife that'll cut you out of your seat belt should it get jammed. It isn't the only one of its kind on the market, but it's cheap, hooks onto your keys, and has this hilarious video to demonstrate its usage. Hit the link for more info.